ByYasser Allawi, Syria DeeplyKaren Leigh, Syria DeeplyMay 16, 2014

A version of this post appeared onSyria Deeply, a multimedia platform covering the Syrian war.

Fighting between extremist factions in eastern Deir ez Zor Province has escalated this week, killing dozens of rebels and forcing residents to flee. At stake is control of a large number of Syria's oil fields, and economic supremacy on the eastern front.

If the north is Syria's bread basket, Deir ez Zor keeps the country fueled. The eastern province, which borders Iraq, has for decades produced the bulk of Syria's crude oil for both domestic consumption and foreign export. The distinction makes the region a top prize for both extremist factions and the Assad government.

Rebels in the province have been fighting each other there for supremacy for months. Islamist brigades initially disagreed over legal provisions of Sharia law, but as battles erupted in areas that contained strategic natural resources, the fight turned to focus on control of Deir ez Zor's oil wells and granaries.

This week, fighting intensified between Jabhat al-Nusra, Al Qaeda's Syrian arm, and the even more extremist Islamic State of Iraq and the Levant (ISIS). Heavy fighting forced civilians to flee by the tens of thousands.

The events underscore the financial importance of Syria's oil. Before the conflict, the country's economic stability depended on oil and agriculture, with oil exports one of its main sources of foreign income. Oil now serves as a financing tool for the rebel fighters who are vying to control it.

ISIS sweeps in

The escalation in Deir ez Zor Province has seen some of the country's fiercest rebel infighting. Clashes first began in Markadeh, a city bordering Deir ez Zor, and the neighboring province of Al Hassakeh, with ISIS prevailing in the early rounds. Riding that momentum, they spread the fight to urban areas; the group, once affiliated with Al Qaeda, now controls the cities of Sour and Busaira as well as the key villages of Jadid Akidat and Tabiat al-Jazira.

On May 4, rebel fighters reached the village of Jadid Bakkara and began negotiations with civilian residents. Saleh, a local opposition fighter, said ISIS arrived and immediately imposed its increasingly conservative restrictions on the village. They stipulated that all Syrian army defectors must surrender; that all males older than 18 must enlist for one year of ISIS military training, then join the fight; and that residents must hand over any remaining members of the Free Syrian Army (FSA) or Jabhat al-Nusra to ISIS for a trial.

The group's arrival and subsequent decree puts civilians in the middle of increasing tensions between ISIS and Jabhat al-Nusra, which has a reputation for taking a softer approach in its dealings with civilians. ISIS, on the other hand, has been known to impose a number of harsh restrictions over civilians in areas under its control, now including Jadid Bakkara. In response to the group's takeover, many of its residents fled.

“Armed men from ISIS attacked the village," says Om Amer, who fled with her family and is now living in another part of the province. "They killed and tortured many of us. They didn’t care if their victims were women, children or old people. The bodies of women and old people are still in the streets. The continuous killing forced us to flee from the village."

"FSA and Jabhat al-Nusra members came to support those of us who opposed ISIS, but they were very late, and in fact, their presence turned the village into hell. So we fled and crossed the Euphrates River to its southern bank," he said.

FSA lends a hand

Hamdi Hassan, a member of the civil defense group in the neighboring village of Muhassan, said his group of volunteer officials received calls for help from the areas where the fighting between ISIS and the other factions was under way. He says moderate opposition groups led by the FSA mobilized to help local civilians.

"FSA members helped the displaced to cross the [Euphrates] river. After that, they were transferred in FSA cars to areas supervised by the local council, which in turn placed them in homes and schools," he says. "During the transfer, we were bombed by the regime’s artillery located at the military airport of Deir ez Zor, which added to the terror that these displaced people were already going through.”

Khalil al-Gharib, vice president of the Local Coordination Council in Deir ez Zor, said the situation in Muhassan has become equally difficult for civilians as the internally displaced arrive from villages like Jadid Bakkara. Thus far, Muhassan has taken in 3,000 people.

"They were placed in homes, schools and what were previously governmental buildings," he says. "The restaurant that provides food for the FSA fighters doubled the number of meals to be distributed to displaced families. Muhassan's proximity to the front lines between the rebels and the regime forces at the Deir ez Zor military airport makes ensuring the needs of all arrivals even more difficult. But the city bears it."

The residents of Muhassan know how it feels to be chased from their homes by rebel infighting: many here were displaced after fighting at the military airport, only eight miles from the center of town. People here say this shared experience moves them to open their homes to the influx of people.

“Our guests are not strangers," says Um Ali, a housewife whose Muhassan home is open to IDPs, showing solidarity in the face of the opposition's fragmentation. "They are Syrians."